Wireless communication technologies are widely used in nowadays. FIG. 1A illustrates the schematic view of a conventional multi-cell wireless communication system 11 adopting Multi-Input and Multi-Output (MIMO) technology. The multi-cell wireless communication system 11 comprises three base stations (BSs) 111, 113, 115 and a mobile station (MS) 117, wherein the BS 115 is the serving BS of the MS 117. Since the BSs 111, 113 are in the neighborhoods of the BS 115 and the MS 117, they will interfere in signal transmissions between the BS 115 because MS 117.
FIG. 1B illustrates another conventional multi-cell wireless communication system 13 adopting MIMO technology, wherein the multi-cell wireless communication system 13 comprises one BS 131, one relay station (RS) 133, and two MSs 135, 137. The MS 135 receives signals from BS 131 directly, while the MS 137 receives signals from the BS 131 through the RS 133. Since the MSs 135, 137 are near the edges of the coverages of the BS 131 and the RS 133, signals transmitted from the RS 133 will interfere in signal transmission between the BS 131 and the MS 135. Likewise, signals transmitted from the BS 131 will interfere in signal transmission RS 133 and the MS 137.
FIG. 1C illustrates yet another conventional multi-cell wireless communication system 15 adopting MIMO technology, wherein the multi-cell wireless communication system 15 comprises three BSs 151, 152, 153, three RSs 154, 155, 156, and two MSs 157, 159. The MS 157 receives signals from the BS 152 directly, while the MS 159 receives signals from RS 155. Since the MSs 157, 159 are near the edges of the coverages of the BS 152 and the RS 155, signals transmitted to the MSs 157, 159 will be interfered in by other BSs and/or RSs.
Since the multi-cell wireless communication systems 11, 13, 15 adopt MIMO technologies, each of the BSs 111, 113, 115, 131, 151, 152, 153 and RSs 133, 154, 155, 156 comprises a plurality of antennas. In MIMO, a signal has to be processed by a precoder before being transmitted by a BS or an RS. To choose a suitable precoder, an MS and an RS has to estimate a channel status for each of the antennas of the serving BS and the neighboring BS and transmit the channel status to the serving BS. The BSs under cooperation will decide the suitable precoder for each of their MSs and RSs, wherein the suitable precoder usually makes the serving BS have the greatest gain and the neighboring BS have less interference to the MS/RS.
In MIMO, a BS allocates reference signals in a predetermined position of a superframe. After receiving the superframe, an MS and an RS can retrieve the reference signals and estimate the channel status accordingly. FIG. 1D illustrates a superframe structure 17 of the IEEE 802.16m standard. When a superframe conforming to the superframe structure 17 is generated by a BS, a frame 171 of the superframe defines a downlink access zone and a downlink relay zone and comprises eight subframes 171a, 171b, 171c, 171d, 171e, 171f, 171g, 171h. Specifically, the downlink access zone comprises subframes 171a, 171b, 171c, 171d, while the downlink relay zone comprise subframes 171e, 171f, 171g, 171h. The second subframe 171b in the downlink access zone is used to allocate a midamble (i.e. the aforementioned reference signal) 170 so that an MS in the coverage of the BS can read the midamble 170 to estimate the channel status. The third subframe 171g in the downlink relay zone is used to allocate another midamble (i.e. the aforementioned reference signal) 172 so that an RS in the coverage of the BS can read the midamble 172 to estimate the channel status. Since an RS is generally fixed relative to a BS, the channel variation is not as fast as an MS, therefore, the appearance frequency of reference signal for an RS needs not to be as often as the one for an MS.
When a superframe conforming to the superframe structure 17 is generated by an RS, a frame 173 of the superframe defines a downlink access zone and a downlink relay zone and comprises eight subframes 173a, 173b, 173c, 173d, 173e, 173f, 173g, 173h. Specifically, the downlink access zone comprises subframes 173a, 173b, 173c, 173d, while the downlink relay zone comprise subframes 173e, 173f, 173g, 1731h. The second subframe 173b in the downlink access zone is used to allocate a midamble (i.e. the aforementioned reference signal) 174 so that an MS in the coverage of the RS can read the midamble 174 to estimate the channel status.
Although there are technologies for transmitting reference signals, current technologies do not support a multi-cell wireless communication system that comprise more than one BSs and more than one RSs. Consequently, there is a need in providing a mechanism that supports a multi-cell wireless communication system that comprises more than one BSs and more than one RSs. In addition, since current technologies reference signals occupies radio resources, there is a need to reduce the reference signals as well.